This application represents a continuing proposal from the Boston Pediatric AIDS Clinical Trials Unit (ACTU), an entity which grew out of a collaboration between ACTUs located at Children's Hospital, Boston City Hospital, and the Brigham and Women's Hospital. During the next four years the Boston PediatriC ACTU will Continue and expand upon its important Contributions to the scientific agenda of the PediatriC ACTG. Investigators will Continue to be active in all phases and at all levels of the pediatric ACTG. Nationally, site investigators will Continue their PACTG committee responsibilities, including leadership roles in the development, design, and ConduCt of trials designed to answer scientific questions critical to the scientific agenda; assist in providing oversight and leadership for the successful implementation and ConduCt of new and ongoing Clinical trials throughout the pediatric ACTG; and provide expertise in the management and evaluation of the pediatric ACTG as a whole. Locally, the Boston Pediatric ACTU Continues its commitment to a Collaborative Pediatric ACTU, Combining the large local and regional referral networks of the Children's Hospital and the Brigham and Women's Hospital with Boston City Hospital's mission of serving inner city residents who have a disproportionate risk of HIV infection. The Boston Pediatric ACTU's Catchment for patient accrual into clinical trials includes 60-70% of Massachusetts' known infected infants and children, plus most of those in Maine, New Hampshire, Vermont, Rhode Island and parts of Connecticut. The Collaborative Pediatric ACTU also Combines the Complementary scientific expertise of its members in the main unit and the two subunits, with proven track- records in the leadership of cliniCal trials in primary therapy and opportunistic infections, the Conduct of studies in the pathogenesis of vertiCal transmission (including obstetriCal CompliCations) and pediatric HIV disease, as well as broad experience in HIV virology and neonatal pharmaCology. The. Boston ACTU plans to submit Competitive appliCations to the PACTG for Core Laboratories in Virology and Pharmacology, and members of the unit plan to Contribute significantly in those scientific disciplines as well.